Heat curable polysiloxane release coatings which stratify when baked and paper coated therewith

ABSTRACT

A heat curable coating composition which deposits a release coating containing a smaller proportion of silicone release material is disclosed. This composition comprises (1) an hydroxy-functional resin which is preferably a polyester resin; (2) a cross-linking agent for the polyester, such as an aminoplast resin; and (3) at least one and preferably a mixture of at least two reactive silicones which are preferably polysiloxanes. These two polysiloxanes comprise: (A) a hydrogen- or alkoxy-functional polysiloxane; and (B) an elastomeric polysiloxane reactive with the hydrogen- or alkoxy-functional polysiloxane to provide release properties. Either or both of the polysiloxanes are reactive with the hydroxy-functional resin or the cross-linking agent. Components (1), (2) and (3) are compatible in a liquid admixture which may contain a volatile inert organic solvent or which may be solvent-free. During the heat cure, the polysiloxanes in component (3) become incompatible with respect to the balance of the composition, and this causes stratification of the polysiloxanes to the surface of the cured coating when the composition is deposited upon a paper or plastic substrate and heated to cure the same. The hydroxy-functional resin and its cross-linking agent go to the paper surface and fill its porosities to minimize the amount of polysiloxane needed to provide the desired release properties.

DESCRIPTION TECHNICAL FIELD

This invention relates to polysiloxane release coatings and includescompositions for coating paper and other substrates in order to providea release surface thereon.

BACKGROUND ART

Reactive organic polysiloxane compositions are known for coating paperin order to provide a release surface thereon. These polysiloxanecompositions are expensive, and it is desired to extend the usefulnessof these materials by providing extended coating compositions which willallow a smaller amount of polysiloxane to effectively coat a givensurface area, and to coat substrates which previously resisted coating.

DISCLOSURE OF INVENTION

In accordance with this invention, a heat curable coating composition isprovided which is adapted to deposit a release coating which stratifiesto allow less silicone (preferably polysiloxane) to effectively coat agiven surface area. This composition comprises: (1) anhydroxy-functional resin which is compatible with the other componentsof the composition, preferably an hydroxy-functional polyester resin;(2) a cross-linking agent for the hydroxy resin, preferably anaminoplast resin, like hexamethoxymethyl melamine; and (3) at least oneand preferably a mixture of at least two reactive silicones. Thesereactive silicones comprise a hydrogen- or alkoxy-functional silicone inwhich the alkoxy group contains from 1-10 carbon atoms. When thepreferred mixture of two reactive silicones is employed, the hydrogen-or alkoxy-functional silicone referred to can be identified as component(A) and the second silicone is; (B) an elastomeric silicone reactivewith the hydrogen- or alkoxy-functional silicone to provide releaseproperties. One or more of the silicones must be reactive with thehydroxy resin and/or the cross-linking agent, and components (1), (2)and (3) are compatible in liquid admixture so that they can be coatedupon a substrate in intimate admixture. The preferred silicones arepolysiloxanes.

The silicones in component (3) become incompatible with respect to thebalance of the composition as reaction proceeds to cause stratificationof the silicone release material to the surface of the cured coatingwhen the composition is deposited upon a substrate and heated to curethe same. This stratification allows the hydroxy resin and itscross-linking agent to concentrate at a paper surface where it can fillany voids in the paper, and it allows the silicone release material toconcentrate at the exposed surface of the coating to provide anonadherent surface using less silicone to effectively cover a givensurface area.

It is also permissible to additionally include other reactive silane orsiloxane materials, such as vinyl- or hydroxy-functional siloxanes, tomodify the release properties as needed for particular utilities, as isknown to the art.

This invention is especially applicable to coating paper, but it is alsoapplicable to plastic surfaces, like terephthalic polyesters (Mylar) andpolypropylene, with a release coating, and the conventional releasecoatings do not adhere well to these surfaces. Some of the releasecoatings of this invention adhere well to these surfaces, sopretreatment of the substrate surface is not needed.

Since this invention can be applied to systems which contain 100% solidsas well as those which contain a liquid thinner enabling application,such as an inert volatile organic solvent, the term "compatible" heredescribes the absence of separation of the components in the liquidcoating composition from one another until after application of thecoating to the substrate. Separation is intended after application, andthis usually accompanies the curing reaction in which the siliconesreact with themselves or one another to increase the molecular weightand complexity of the silicone component to force the silicones toseparate from the hydroxy-functional resin. This separation orstratification is easily detected in the cured coating by the highconcentration of silicone at the exposed surface of the coating.

From the standpoint of the coated product, the hydroxy-functional resinand its curing agent are concentrated at the substrate surface (in andaround the porosities of the paper usually used) and the reactedsilicones are concentrated at the exposed surface. Between theseconcentrations is a gradient in which all of the components (1), (2) and(3) are present and reacted with one another.

Component (3) cannot be deposited upon a previously deposited layer ofcomponents (1) and (2), for the use of two treatments is uneconomicaland, if tried, it would be hard to meter the small amount of thesilicone coating. Also, when platinum catalysts are used, there wouldnot be sufficient chemical combination between the polysiloxanes andcomponents (1) and (2) to provide good intercoat adhesion, unless somespecial treatment is employed. As a result, when the release coatedpaper is subsequently coated with adhesive and adhered to label stock(or adhered to adhesive-coated label stock), removal of the label stockwith its adhesive surface would remove some of the silicone layer.Wherever the silicone is removed, it covers the adhesive surface of thelabel, preventing it from there sticking to a substrate against which itis applied.

This invention seeks to provide a combination in which little,preferably 0%, of the adhesive surface is covered with polysiloxane whenthe adhesively coated label is removed.

One must also provide a release coating which is fully effective overthe entire surface of the supporting paper stock. If some portion of thepaper is not provided with good release properties, then some of theadhesive which should remain with the label will instead stay with thesupporting paper when the adhesively coated label is removed. Again, theadhesively coated label will be incompletely adhered to the substrate towhich it is applied, assuming the label can be removed in the firstplace.

In the previous efforts to provide release coated paper of the characterunder consideration, it was necessary to employ from 0.5 to 1.0 poundsof silicone per ream of paper. The smaller proportions within the rangeare useful when very smooth paper stock, such as supercalandered paper,is employed. It is found that one can usually obtain equivalent releaseproperties using about one-fourth of the amount of the silicone materialpreviously employed.

Also, and since much smaller proportions of expensive polysiloxanes areuseful herein, one can employ less costly and more porous paper stock tosupport the silicone release coating. This is because stratificationcauses the hydroxy resin and cross-linking agent therefor to concentrateat the paper surface to fill the porosities in the paper.

This invention is preferably carried out using two different types ofcompositions. The choice between these compositions depends upon whetherthe coater who applies the composition will tolerate the presence ofvolatile organic solvent.

The hydroxy-functional resin, sometimes termed the hydroxy resin, may beany resin having sufficient hydroxy functionality for cure and which iscompatible with the other components of the coating composition untilafter application. Polyester resins are preferred, and these will bediscussed hereinafter. Other hydroxy functional resins which may be usedare illustrated by copolymer of monoethylenically unsaturated monomers,such as a solution copolymer of 15% 2-hydroxyethyl acrylate, 40% laurylmethacrylate and 45% styrene, methyl methacrylate or a mixture thereof.Copolymers of vinyl acetate hydrolyzed to 50% hydroxy content, with halfof these hydroxy groups being esterified with stearic acid, may also beused.

Referring more particularly to a preferred composition which can beapplied at 100% solids content so that volatile organic solvents are notneeded, this composition comprises: (1) a low molecular weightsufficiently fluid for coating application) polyester resin of highhydroxy-functionality (hydroxy number of at least about 100) preferablymodified with an unsaturated oil, such as a safflower oil-modified alkydresin; (2) a cross-linking agent for the polyester, as previouslydescribed; and (3) a mixture of two reactive polysiloxanes comprising:(A) a hydrogen- or alkoxy-functional polysiloxane; and (B) anelastomeric vinyl- or hydroxy-terminated polysiloxane which reacts withthe hydrogen- or alkoxy-functional silicone to provide releaseproperties.

Using the hydrogen-functional polysiloxane as illustrative, the hydrogengroups of the hydrogen-functional polysiloxane are reactive with thevinyl groups in the vinyl-terminated polysiloxane and also with theunsaturation in the unsaturated oil. This reaction is catalyzed with aplatinum catalyst, such as chloro platinic acid. The hydrogen groups ofthe hydrogen-functional polysiloxane are also reactive with the hydroxyfunctionality in the hydroxy resin. The hydroxy groups of the hydroxyresin are reactive with the preferred aminoplast cross-linking agent,and an acid catalyst, such as dodecyl benzene sulfonic acid, is used toencourage this reaction. These several reactions thermoset thestratified release layer at the exposed coating surface and provide theadhesion between the stratified layers which is desired. To furtherimprove the adhesion between the layers, silane coupling agents can beadded to the mixture of components (1), (2) and (3), these couplingagents being usually trimethoxy silanes containing an amine, mercaptanor epoxy functional group as the fourth substituent on the silanesilicon atom, as is known.

The hydrogen groups of the hydrogen-functional polysiloxane are alsoreactive with hydroxy groups in a hydroxy-terminated polysiloxane, andthis reaction is catalyzed with a metal salt where the metal ion isselected from the lead to manganese electromotive force series. Thisseries of metal catalysts is well known and is illustrated by a tin saltof a monocarboxylic or dicarboxylic acid, such as dibutyl tin diacetate.

One can employ hydroxy-functional polyester resins and polysiloxanes ofrelatively low molecular weight. These materials are liquids which floweasily to enable coating application in the absence of volatile solvent.Some coaters insist that such solvent be entirely absent, and a typicalcomposition which can be used in the absence of solvent will beillustrated hereinafter. Of course, some coaters will tolerate a smallamount of organic solvent, and in such instances a small amount ofsolvent can be used to adjust viscosity. Thus, these compositions arepreferably used in the substantial absence of volatile organic solvent.

Components (1), (2) and (3) in the above composition are compatible inliquid admixture, and the polysiloxanes in component (3) becomeincompatible with respect to the balance of the composition as thecuring reactions proceed to cause stratification of the polysiloxanerelease material to the surface of the cured coating when thecomposition is deposited upon a paper or other substrate and heated tocure the same.

Some coaters will tolerate the presence of significant proportions oforganic solvent, and this enables the utilization of polysiloxanes ofhigher molecular weight which are not sufficiently fluid to provide acomposition which can be applied in the absence of solvent. In suchinstance, this invention can be practiced with an alternative type ofcomposition comprising: (1) a more viscous hydroxy resin which ispreferably a more highly branched hydroxy-functional polyester resinthan in the solvent-free composition, as by the presence therein of acomponent having a functionality of at least 3, like pentaerythritol;(2) a cross-linking agent for the polyester, as previously described;and (3) a mixture of at least two reactive polysiloxanes. These tworeactive polysiloxanes comprise: (A) a hydrogen- or alkoxy-functionalpolysiloxane; and (B) a high molecular weight elastomeric hydroxy- orvinyl-terminated polysiloxane reactive with the hydrogen-functionalsiloxane to provide release properties.

To illustrate the action when a hydroxy-terminated polysiloxane isemployed, it is reactive with aminoplast resin cross-linking agents. Theacid catalyst relied upon to encourage the cure between the polyesterresin and the aminoplast resin also encourages reaction between thehydroxy-functional polysiloxane and the aminoplast resin. This helps toprovide adhesion between the stratified layers of the cured coating. Thehydrogen groups of the hydrogen-functional polysiloxane are alsoreactive with the hydroxy groups present in both the polyester resin andthe hydroxy-functional polysiloxane. These reactions are catalyzed withthe previously described metal salt catalysts, such as dibutyl tindialurate. These reactions serve to aid adhesion between the stratifiedlayers and to thermoset the release layer at the exposed surface.

To illustrate the action when a vinyl-terminated polysiloxane isemployed, the hydrogen groups of the hydrogen-functional polysiloxaneare reactive with the vinyl groups of the vinyl-functional siloxane andthe hydroxy groups present in the polyester resin. These reactions arecatalyzed with platinum and acid catalysts and serve to thermoset therelease layer at the exposed surface and to aid adhesion between thestratified layers.

This type of composition can tolerate polyester resins and hydroxy- orvinyl-functional polysiloxanes which are highly viscous or even solid atroom temperature (25° C.) and sufficient non-reactive volatile organicsolvent can be added to provide the fluidity needed for coatingapplication.

Components (1), (2) and (3) in the above composition are compatible inthe solvent solution coating composition, and the polysiloxanes incomponent (3) become incompatible with respect to the balance of thecomposition as the solvent is vaporized away and the curing reactionproceeds, as previously described.

As will be evident, heat is employed to speed the removal of solvent, ifit is present, and this heat is relied upon to force the various curingreactions which have been specified to proceed to cure the compositionin a reasonable period of time.

Water application is also permissible. Carboxyl-functional polyesters orcopolymers having an acid value of from 30 to 150 can be dispersed inwater with the aid of a volatile base, such as ammonia, and the siliconematerials can be added as aqueous emulsions, as illustrated in U.S. Pat.Nos. 2,588,367 and 3,900,617. While one may include acid-functionalpolyesters or copolymers, as noted above, it is also possible to usepolyesters or copolymers having very little acid content and an hydroxylvalue of from about 50 to about 250, preferably from 100 to 200. Thesecan be dispersed in water together with the melamine resin curing agentusing simple agitation and without the addition of any base. Thus, thehexamethoxymethyl melamine can be dissolved in the water after theaddition of the polyester or copolymer, or together therewith. In thisway, water can be used to replace all or most of the volatile organicsolvent.

The polyesters which are used herein are hydroxy-functionalpolyesterification products of polycarboxylic acids with polyalcohols,the polyalcohol being used in stoichiometric excess over the carboxylfunctionality present to provide hydroxy groups for subsequent cure. Anhydroxy number of from about 40 to about 250, preferably from 100 to200, is appropriate. Typical polycarboxylic acids are phthalic acid,adipic acid, and their anhydrides. Typical polyalcohols are glycerine orbutane diol. The production of polyesters and their components arecommon knowledge in polymer chemistry.

When the polyester is to be used in solvent-free compositions, it shouldbe a low molecular weight polyester which is a free flowing liquid atroom temperature to be useable in the absence of more than 5% ofvolatile organic solvent, based on total resin solids present. Thesepolyesters may be modified with an unsaturated oil or fatty acid derivedtherefrom, so as to contain ethylenic unsaturation providing an iodinenumber of at least 30, preferably at least 80, for cure. The usual oilmodified alkyd resins are formed by reacting an unsaturated oil of fattyacid therefrom, such as safflower oil, linseed oil, dehydrated castoroil, soya oil or a fatty acid derived therefrom, with glycerin andphthalic anhydride. A small amount of maleic anhydride is usuallyincluded to assist polyester formation.

The cross-linking agent for the hydroxy resin may be anything having aplurality of groups reactive with the hydroxy groups of that resin. Thepreferred cross-linking agent is an aminoplast resin, likehexamethoxymethyl melamine, and the aminoplast cure ofhydroxy-functional resins is conventional and is commonly speeded withan acid catalyst. These catalysts are well known. Para toluene sulfonicacid is a common useful catalyst, and this known class of catalysts isalso illustrated in the Examples. Hexamethoxymethyl melamine ispreferred because it is liquid at room temperature and helps to minimizethe proportion of solvent.

Other cross-linking agents for hydroxy-functional resins are also wellknown, and are best illustrated by phenoplast resins, such as theconventional solvent-soluble phenol-formaldehyde condensates. Tertiarybutyl phenol or cresol may be used in place of the phenol in thesecondensates. Organic polyisocyanates which are blocked to preventprereaction are also useful, and these are illustrated by the diurethanereaction product formed by reacting two moles of 2-ethyl hexanol withone mole of 2,4-toluene diisocyanate or isophorone diisocyanate.Aminoplast cross-linking agents, phenoplast cross-linking agents andblocked polyisocyanate cross-linking agents are all known for the cureof hydroxy-functional resins.

The reactive silicones (polysiloxanes) which cure to provide a releasecoating are themselves known. With reference to the use of mixtures,which is preferred, any curable mixture of a hydrogen- oralkoxy-functional polysiloxane and an elastomeric polysiloxane carryinggroups reactive with the Si-H or Si-OR groups of the polysiloxane may beused. R denotes an alkyl or alkoxyalkyl group containing from 1 to 10carbon atoms. When the substantial absence of organic solvent isdesired, the reactive polysiloxanes will comprise: (A) a hydrogen- oralkoxy-functional polysiloxane; and (B) an elastomeric polysiloxanereactive with the hydrogen- or alkoxy-functional polysiloxane to providerelease properties. As previously indicated, other silicone or silanematerials may be added, but this is not essential.

The Si-H or Si-OR groups are reactive in various ways. The Si-H groupsof the hydrogen-functional polysiloxane are reactive with theunsaturation and hydroxy functionality in the oil-modified polyesterresin, and with the polysiloxane if it carries unsaturated groups (vinylgroups) or hydroxy groups. This reaction between Si-H and ethylenicunsaturation is known and is normally catalyzed by a platinum-typecatalyst. The reaction with hydroxy groups is also known and is normallycatalyzed by a metal salt catalyst, as previously illustrated. Thealkoxy functionality which may be selected is reactive with hydroxyfunctionality in the polyester resin and in the polysiloxane, and thetin-type catalyst assists these reactions.

The hydrogen-functional polysiloxane, the alkoxy-functionalpolysiloxane, the hydroxy-functional polysiloxane, and thevinyl-functional polysiloxane are all available in commerce as easilyflowable liquid resins. This enables these to be used in a liquidmixture which is easily applied as a coating on a paper substrate in thesubstantial absence of organic solvent.

All of the above components are compatible in liquid admixture, andsolvent is not needed to provide compatibility. When the liquid coatingcomposition is applied as a coating and heated to cause the componentsof the coating to react, the polysiloxanes grow in molecular weight andcomplexity and become incompatible with respect to the balance of thecomposition. This causes stratification of the polysiloxane releasematerial to the surface of the cured coating, and this allows thehydroxy resin and its cross-linking agent to concentrate at the papersurface where it can fill the voids of the paper to reduce the amount ofneeded polysiloxane.

Significant proportions of volatile organic solvent enable the use ofresins which are not sufficiently fluid for application in the absenceof solvent. The capacity to use a higher molecular weight less fluidhydroxy resin, e.g., the polyester resin which is preferred, allows oneto employ hydroxy-functional resins which may be of higher molecularweight or more highly branched. This is preferably accomplished byincluding in the materials subject to polyesterification a componenthaving a functionality of at least 3, such as a trihydric acid, liketrimellitic anhydride, or a polyol of higher functionality, liketrimethylol propane or pentaerythritol. Suitable branchedhydroxy-functional polyester resins will be illustrated in the examples.Since these are more viscous than those used in the absence of solvent,a somewhat lower hydroxy number of about 40 may be used, and this isabout the least hydroxy functionality which can be used in the hydroxyresin.

The cross-linking agent for the more viscous polyester resins is thesame as is used for the less viscous oil-modified polyesters. However,unsaturation is no longer needed, so the polyester need not beoil-modified, or if oil-modified, the fatty acid or oil may besaturated.

The two reactive polysiloxanes may now be of somewhat differentcharacter because the presence of organic solvent now allows the use ofhigher molecular weight polysiloxanes to provide the elastomeric releaselayer. The hydrogen-functional polysiloxane is much the same as was usedpreviously, but the elastomeric polysiloxane need no longer be arelatively low molecular weight material, and one can instead employrelatively high molecular weight polysiloxanes in which the reactivegroups are preferably hydroxyl groups or vinyl groups which are usuallysupplied by having one such group at each end of the molecule, butlarger numbers of reactive groups are also useful.

The hydrogen groups of the hydrogen-functional siloxane are reactivewith the hydroxy groups which are present in the hydroxy resin and inthe hydroxy-functional polysiloxane, and also with the vinyl groupswhich are present in the vinyl-functional polysiloxane, and thesereactions are catalyzed with acid and tin-type or platinum catalyst, aspreviously noted.

Sufficient non-reactive volatile organic solvent is added to provide thefluidity or compatibility needed for coating application, and usefulsolvents are common knowledge. Any solvent, such as methyl ethyl ketone,2-ethoxy ethanol acetate, heptane, chlorinated hydrocarbons, liketrichlorethylene, butyl acetate, toluene or xylene, may be used.Hydrocarbon solvents are preferred for the higher molecular weightpolysiloxanes. Suitable solvents are further illustrated in theExamples.

Referring more particularly to the elastomeric vinyl-terminatedpolysiloxane having release properties, these can be described asorganosilicone polymers having an average of from one to three groupsper silicon atom selected from the group consisting of monovalenthydrocarbon radicals, free of acetylenic unsaturation, monovalenthalohydrocarbon radicals, free of aliphatic unsaturation, and cyanoalkylradicals, there being at least one terminally unsaturated monovalentolefin radical per molecule, the remaining valences of the silicon atomsof the said organosilicon polymer being satisfied by selection from thegroup consisting of divalent oxygen atoms, divalent hydrocarbonradicals, free of acetylenic unsaturation, divalent hydrocarbon etherradicals, free of acetylenic unsaturation, and divalent haloaryleneradicals, said divalent radicals linking silicon atoms.

The optional polysiloxanes which may be present are illustrated bypolysiloxane terpolymers which can be described as an organosiliconresin consisting of R₃ SiO1/2, R₂ SiO and SiO4/2 units in which the Rgroups may be the same or different and selected from hydrogen, hydroxy,alkyl, aryl, aralkyl, alkaryl, alkenyl, cycloalkyl, cycloalkenyl groups.It is preferred to have all or most of the R groups constituted bymethyl groups, as is well known, but phenyl groups are also available.

Referring more particularly to the hydroxy-functional polysiloxaneswhich may be used herein, these can be described as an organosiliconcompound containing at least one silicon-bonded hydroxy group permolecule, there being in addition an average of up to two groups persilicon atom selected from the group consisting of monovalenthydrocarbon radicals free of aliphatic unsaturation, monovalenthalohydrocarbon radicals free of aliphatic unsaturation, and cyanoalkylradicals, the remaining valences of the silicon atoms being satisfied bygroups selected from the group consisting of divalent oxygen atoms,divalent hydrocarbon radicals, free of aliphatic unsaturation, divalenthydrocarbon ether radicals free of aliphatic unsaturation, and divalenthaloarylene radicals, said divalent radicals linking silicon atoms.

The sum of the average number of terminally unsaturated monovalentolefin radicals per molecule of the vinyl-terminated silicone or theaverage number of hydroxy groups per molecule of the hydroxy-terminatedsilicone, and the average number of silicon-bonded hydrogen atoms permolecule of the hydrogen-functional silicone or the alkoxy-functionalsilicone, is greater than 3.

It is preferred for these silicones to be organopolysiloxanes, usuallymethyl-substituted. The hydrogen-functional silicone is most preferablya methyl-substituted organopolysiloxane having an average of 3 to 75silicon-bonded hydrogen atoms per molecule.

The preferred hydrogen-functional silicones are organopolysiloxaneshaving an average of 3 to 75 silicon-bonded hydrogen atoms per moleculeand having a viscosity of from about 2 to about 100 centipoises and amolecular weight of about 330 to about 5000. A product having aviscosity of 30 centipoises and a molecular weight of 2270 isparticularly useful.

The alkoxy-functional silicones may be monomers or disiloxane compoundsof polymeric compounds, such as silicates, polysilicates, or polyalkoxypolysiloxanes resulting from the partial hydrolysis of monomers of theformula Si(OR)₄ and/or R'Si(OR")₃, where R, R' and R" are alkyl oralkoxyalkyl containing from 1 to 10 carbon atoms, preferably from 1 to 4carbon atoms.

It is preferred to use polyalkoxy polysiloxanes containing from 3 to 75alkoxy groups per molecule.

The preferred vinyl-terminated silicone is also the same as thehydrogen-functional polysiloxanes, except that in place of the Si-Hgroups, we have a smaller number of ethylenically unsaturated groups,e.g., vinyl groups. These vinyl-terminated silicones are most preferablyan organopolysiloxane having an average of from 1.98 to 2.05 groups persilicon atom which are selected from the group consisting of vinyl,methyl, phenyl and 3,3,3-trifluoropropyl and having an average of from 2to 5 vinyl groups per molecule.

The preferred hydroxy-functional polysiloxanes are again the same as thehydrogen-functional polysiloxanes, except that the Si-H groups arereplaced by a smaller number of hydroxy groups which may be carrieddirectly by the silicon atoms or which may be carried by hydrocarbongroups which terminate in the alcoholic hydroxyl group.

The vinyl-terminated polysiloxane and the hydrogen-functionalpolysiloxanes are catalyzed by a platinum catalyst in an amount of atleast 0.5 part per million of platinum based on the combined weights ofthe two silicone materials. The optional polysiloxane, if present, wouldbe catalyzed in accordance with its reactivity, as has been described.

Any platinum catalyst can be used, for example platinum deposited oncharcoal or alumina, chloroplatinic acid, or the reaction product ofchloroplatinic acid and olefins or organosilicon compounds containingolefin radicals. In place of the platinum catalyst, one can use rhodiumcatalysts, as pointed out in U.S. Pat. No. 3,928,629 which disclosessulphur-containing rhodium complexes and rhodium-carbonyl complexes. Anillustrative rhodium catalyst has the formula: RhCl₂ (Bu₂ S)₃. Also, theplatinum catalyst can be replaced by ruthenium, rhodium, palladium,osmium, and iridium, or a complex containing these metals.

Silicone compositions of the type described above are known and aredisclosed in U.S. Pat. Nos. 2,823,218 and 3,249,581. Also, and to renderthe compositions more stable on admixture, one may also include anorganic compound having a boiling point of at least 25° C. and at leastone --C.tbd.C-- group, said organic compound being free of nitrogen,carboxyl, phosphorus, mercapto groups, and carbonyl groups which arealpha to aliphatically unsaturated carbon atoms, there being at least 2times the moles of --C.tbd.C-- present as the moles of platinum present.The compositions containing the two silicone materials, the platinumcatalyst, and including the acetylenic group-containing organic compoundwhich are preferably secondary or tertiary alcohols, like2-ethynyl-isopropanol, 3,5-dimethyl-1-hexyne-3-ol, isopropenylacetylene,and 2-ethynyl-butane-2-ol are more fully described in U.S. Pat. No.3,445,420, the disclosure of which is incorporated herein by reference.

In place of the acetylenic organic compound one can use diallyl maleateto render the catalyst less prone to rapidly gel the composition priorto use. This is shown in U.S. Pat. No. 4,256,870.

Referring more particularly to the high molecular weight elastomerichydroxy- or vinyl-functional polysiloxane having release properties,these are hydroxy- or vinyl-terminated silicones, preferablypolysiloxanes, which have sufficient molecular weight to be viscousliquids. It is the excessive viscosity of these liquids for normalcoating application which requires that a proportion of organic solventbe used to reduce the viscosity and enable application. Thesepolysiloxanes are preferably dihydric or divinylic, since these are mostreadily available in commerce. Typical polysiloxanes which are availableat 100% solids have a room temperature viscosity in excess of about3,000 centipoises and are dimethyl polysiloxanes, except for the twoterminal silicon atoms which also carry a single hydroxy group. Thesehydroxy terminated silicones are sometimes sold in combination withhydrogen-functional polysiloxanes.

The invention will be illustrated in the following Examples, it beingunderstood that throughout this application, all parts and proportionsare by weight unless otherwise stated.

EXAMPLE 1

The components listed below were mixed together to provide an off-white,milky liquid having a pot life of about 4-6 hours. Two formulas wereprepared, as indicated the Table.

                  TABLE                                                           ______________________________________                                        Component            I       II                                               ______________________________________                                        1-alkyd-melamine blend                                                                             100     100                                              2-vinyl-terminated polysiloxane                                                                    13.9    23.1                                             (see note 1)                                                                  3-hydrogen-functional                                                                              1.8     3.0                                              polysiloxane (see note 2)                                                     4-dodecyl benzene sulfonic acid                                                                    5.2     5.8                                              ______________________________________                                    

The two compositions set forth above were both fully effective, exceptcomposition II which contained a larger proportion of polysiloxanerelease material produced a somewhat stronger release action.

These liquids are used by applying them as a coating upon paper in atypical weight of about 1.5 pound per ream (3000 square feet). Theapplied coating is then cured by passing it through an oven maintainedat 140° C. for 30 seconds. At this cure schedule the cure is rapid andone can shortly thereafter overcoat the cured coating with adhesive. Ifa lesser curing schedule is used, such as 120° C. for 30 seconds, thenit is desirable to allow the coating to age for at least 24 hours toinsure that the siloxanes have reasonably completely reacted with oneanother to make sure that the applied adhesive is completely released bythe release coating when a label which is subsequently adhered to theadhesive is removed for use.

Note 1: A vinyl-terminated polydimethylsiloxane having a roomtemperature viscosity of 300 centipoises which may be the Dow Corningproduct SYL OFF 7600, formerly sold as Q2-7203.

Note 2: A hydrogen-functional polymethylsiloxane polymer having a roomtemperature viscosity of 35 centipoises which may be the Dow Corningproduct SYL OFF 7601, formerly sold as Q2-7220.

The alkyd resin used in the above composition is made by heating amixture of 650 grams of safflower oil and 137 grams of glycerine to 232°C. in the presence of 0.3 gram of reagent grade sodium hydroxide tocatalyze an alcoholysis reaction. Alcoholysis is considered complete ifa clear solution results when 1 part of alcoholysis product is mixedwith either 4 parts of methanol or 1 part of melted phthalic anhydride.About 1/2 to 1 hour is required to carry out the alcoholysis reaction.

After the reaction mixture is cooled to 140° C., 57 grams of phthalicanhydride and 100 grams of adipic acid are added, and 19 grams of xyleneare added to allow water of reaction to be removed by azeotropicdistillation. The mixture is then heated slowly to 220° C. and held atthis temperature until the polyesterification reaction is complete, asindicated by an acid value of less than 5. The contents of the receiverused to trap water are then removed and most of the remaining xylene areremoved by passing dry nitrogen gas through the hot material for 1/2hour. The batch was cooled and processed neat to provide an alkyd resinof relatively low molecular weight (Gardner-Holdt viscosity of R), thenumber average molecular weight is about 805.6. The solids content was98.31%, so there is little solvent present, and the acid value was 2.8.The hydroxyl value (theoretical) is 136.5.

To provide the alkyd-melamine blend which is used in this Example, 100parts of the above alkyd resin are mixed with 55 parts ofhexamethoxymethyl melamine (American Cyanamid product Cymel 301 may beused) at room temperature.

EXAMPLE 2

125 grams of glycerin, and 1085 grams of stearic acid, are heated to100° C. and then 66 grams of benzoic acid and 400 grams ofpentaerythritol are added. The mixture is heated to 230° C. in thepresence of 50 grams of xylene to enable azeotropic removal of water.After the theoretical water (78 ml.) is collected in about 1/2 hour, thebatch is cooled to 160° C. and 50 grams of glycerin, 82 grams ofpentaerythritol, 12 grams of maleic anhydride and 738 grams of phthalicanhydride are added. The mixture is heated to 220° C. while collectingwater and held at that temperature until the acid value is below 10.After cooling to 100° C., toluene was added to a solids content of 60%.The product has a Gardner-Holdt viscosity of Z1, an acid number of 7.88,an hydroxy number of 134.5, and a number average molecular weight of3140.

100 pounds of the above polyester resin solution at a temperature of85°-110° F. has added thereto 36 pounds of hexamethoxymethyl melamine(American Cyanamid product Cymel 303 may be used), 57.9 pounds oftoluene and 18.4 pounds of aliphatic hydrocarbon solvent having aboiling range of 350°-386° F. (Exxon product Isopar K may be used).There is then separately premixed 3.88 pounds of dodecyl benzenesulfonic acid catalyst (American Cyanamid product Cycat 600 may be used)with 0.86 pounds of 2-amino-2-methyl-1-propanol. When the exothermsubsides, this catalyst solution is added to the previously describedmixture, which is then strained into drums for storage.

To 100 pounds of solution stir in 54.3 pounds of the previouslyspecified aliphatic hydrocarbon solvent and then sequentially add 7.1pounds of a preformed mixture containing 30% solids in xylene, thesolids being 94% dihydroxy-terminated polydimethylsiloxane providing the30% solution with a room temperature viscosity of 30,000 centipoises,and 4% of a hydrogen-functional polymethyl hydrogen polysiloxane havinga room temperature viscosity of about 30 centipoises similar to thehydrogen-functional polymethylsiloxane polymer used in Example 1. Thereis then added 0.74 pounds of a dihydroxy polydimethylsiloxane (100%solids) having a viscosity of 12,500 and 0.53 parts of dibutyl tindiacetate (Dow Corning catalyst 176 may be used). This mixture has a potlife greater than 8 hours. When coated upon paper at about 1.0 pound perream and cured at 150° C. for 30 seconds, it provides a coated paperhaving good release properties.

The release properties and the intercoat adhesion of this coating can beenhanced by adding to the composition 0.74 pounds of an epoxy-functionalsilane, such as Dow Corning product SYL OFF 297.

The compositions of these examples are also adherent to Mylar andpolypropylene.

EXAMPLE 3

Example 2 is repeated using in place of the 7.1 pounds of 30% solidsxylene solution, a solution in which the solids are supplied by amixture of:

45% alpha, omega, di(hydroxyl)-methylvinyl polysiloxane oil containing95% (CH₃)₂ SiO units, 5% CH₂ (CH₂ ═CH)SiO units and having a viscosityof 500 mPa.s at 25° C.;

45% methylpolysiloxane oil having a viscosity of 75 mPa.s at 25° C. andcontaining 25% CH₃ SiO₁.5 units, 72.5% (CH₃)₂ SiO units and 2.5% of(CH₃)₃ SiO₀.5 units and having 1.8% by weight of hydroxyl groups; and

10% of silane having the formula CH₂ ═CHSi(OCH₂ CH₂ OCH₃)₃.

Corresponding results are obtained.

EXAMPLE 4

The components specified below are mixed together to provide anoff-white, milky liquid having a pot life of about 6-8 hours.

alkyd-melamine blend (same as Example 1): 100 parts

hydrogen-functional polysiloxane (Note 3): 20 parts

dodecylbenzene sulfonic acid: 1.3 parts

dibutyl tin diacetate: 0.5 parts

This liquid is used by applying it as a coating upon paper in a typicalweight of about 1.5 pounds per ream. The applied coating is then curedby passing it through an oven maintained at 150° C. for 60 seconds.

Note 3: A hydrogen-functional polymethylsiloxane polymer having a roomtemperature viscosity of 30 centipoises which may be the Dow Corningproduct 1107 fluid.

EXAMPLE 5

The components listed below are mixed together to provide an off-white,milky liquid.

alkyd melamine blend: 55 parts alkyd;

(Alkyd of Example 1): 25 parts Cymel 350

aqueous silicone emulsion (Note 4): 40 parts

dodecylbenzene sulfonic acid: 5.7 parts

dibutyl tin diacetate: 4.0 parts

The mixture has a pot life of about 4 hours. When coated upon paper atabout 1.0 pounds per ream and cured at 150° C. for 60 seconds, itprovides coated paper with good release properties.

Note 4: The aqueous silicone emulsion is a 50% solids emulsion in water,the solids being 95% dihydroxy-terminated polydimethylsiloxane having aviscosity of 300,000 centipoises and 5% of a hydrogen functionalpolymethyl siloxane polymer having about 35 Si-H groups, and a viscosityof 30 centipoises. (The Dow Corning product 1171A may be used.)

What is claimed is:
 1. A heat curable coating composition adapted todeposit a release coating which stratifies to allow less silicone tocoat a given surface area comprising:(1) an hydroxy-functional resin;(2) a cross-linking agent for the hydroxy-functional resin; and (3) atleast one reactive silicone resin to provide release properties,saidsilicone resin being reactive with the hydroxy resin or thecross-linking agent, and components (1), (2) and (3) being compatible inliquid admixture.
 2. A coating composition as recited in claim 1 inwhich a mixture of at least two reactive silicones is employedcomprising:(A) a hydrogen- or alkoxy-functional silicone in which thealkoxy group contains from 1-10 carbon atoms; and (B) an elastomericsilicone reactive with said hydrogen or alkoxy-functional silicone toprovide release properties,either or both of said silicones beingreactive with the hydroxy resin or the cross-linking agent, andcomponents (1), (2) and (3) being compatible in liquid admixture.
 3. Acoating composition as recited in claim 2 in which said silicones arepolysiloxanes, and said component (3) (B) is an elastomeric vinyl- orhydroxy-terminated polysiloxane.
 4. A coating composition as recited inclaim 3 in which said component (3) (A) is a hydrogen-functionalpolysiloxane.
 5. A coating composition as recited in claim 3 in whichthere is also present a siloxane terpolymer consisting of R₃ SiO1/2, R₂SiO and SiO4/2 units in which the R groups may be the same or differentand selected from hydrogen, hydroxy, alkyl, aryl, aralkyl, alkenyl,cycloalkyl, and cycloalkenyl groups.
 6. A coating composition as recitedin claim 2 in which the silicones in component (3) react with each otherto become incompatible with respect to the balance of the composition ascure proceeds to cause stratification of the silicones to the surface ofthe cured coating when the composition is deposited upon a papersubstrate and heated to cure the same.
 7. A coating composition asrecited in claim 1 in which said cross-linking agent is an aminoplastresin.
 8. A coating composition as recited in claim 7 in which saidaminoplast resin is hexamethoxymethyl melamine.
 9. A coating compositionas recited in claim 7 in which said composition includes an acidcatalyst to encourage reaction of the hydroxy groups on said hydroxyresin with said aminoplast resin.
 10. A coating composition as recitedin claim 2 in which said component (3) (A) is a hydrogen-functionalsilicone which is an organosilicon compound containing at least onesilicon-bonded hydrogen atom per molecule, there being in addition anaverage of up to two groups per silicon atom selected from the groupconsisting of monovalent hydrocarbon radicals free of aliphaticunsaturation, monovalent halohydrocarbon radicals free of aliphaticunsaturation, and cyanoalkyl radicals, the remaining valences of thesilicon atoms being satisfied by groups selected from the groupconsisting of divalent oxygen atoms, divalent hydrocarbon radicals, freeof aliphatic unsaturation, divalent hydrocarbon ether radicals free ofaliphatic unsaturation, and divalent haloarylene radicals, said divalentradicals linking silicon atoms.
 11. A coating composition as recited inclaim 10 in which said hydrogen-functional silicone is amethyl-substituted polysiloxane having an average of 3 to 75silicon-bonded hydrogen atoms per molecule.
 12. A coating composition asrecited in claim 2 in which said elastomeric silicone is avinyl-terminated silicone.
 13. A coating composition as recited in claim12 in which said vinyl-terminated silicone is a polysiloxane having anaverage of from 1.98 to 2.05 groups per silicon atom which are selectedfrom the group consisting of vinyl, methyl, phenyl, and3,3,3-trifluoropropyl, and having an average of from 2 to 5 vinyl groupsper molecule.
 14. A coating composition as recited in claim 3 in whichsaid elastomeric polysiloxane is a hydroxy-terminated polysiloxanehaving an average of from 1.98 to 2.05 groups per silicon atom which areselected from the group consisting of vinyl, methyl, phenyl, and3,3,3-trifluoropropyl, and having an average of from 2 to 5 hydroxygroups per molecule.
 15. A coating composition as recited in claim 3 inwhich said component (3) (A) is an alkoxy-functional polysiloxane.
 16. Acoating composition as recited in claim 15 in which saidalkoxy-functional polysiloxane is a monomer silane or a polymer obtainedby the partial hydrolysis of the silicates of the formula Si(OR)₄ and/orR'Si(OR")₃ in which the symbols R, R' and R" denote an alkyl or alkoxyalkyl group containing from 1 to 10 carbon atoms.
 17. A coatingcomposition as recited in claim 1 in which said hydroxy resin is a lowmolecular weight polyester resin having an hydroxy number of from about50 to about
 250. 18. A coating composition as recited in claim 17 inwhich said polyester resin is modified with an unsaturated oil or fattyacid derived therefrom.
 19. A heat curable coating composition which issubstantially free of volatile organic solvent and which is adapted todeposit a release coating which stratifies to allow less polysiloxane tocoat a given surface area comprising:(1) a low molecular weightpolyester resin having a hydroxyl value of at least about 100 modifiedwith an unsaturated oil; (2) a cross-linking agent for the polyester;and (3) a mixture of at least two reactive polysiloxanes comprising:(A)a hydrogen- or alkoxy-functional polysiloxane in which the alkoxy groupcontains from 1-4 carbon atoms; and (B) an elastomeric vinyl- orhydroxy-terminated polysiloxane reactive with said hydrogen- oralkoxy-functional polysiloxane to provide release properties,said vinyl-or hydroxy-terminated polysiloxane being reactive with the unsaturationof said polyester resin, and components (1), (2) and (3) beingcompatible in liquid admixture.
 20. A coating composition as recited inclaim 19 in which said oil-modified polyester resin is a safflower oilalkyd.
 21. A coating composition as recited in claim 19 in which saidcross-linking agent is an aminoplast resin.
 22. A coating composition asrecited in claim 21 in which said aminoplast resin is hexamethoxymethylmelamine.
 23. A coating composition as recited in claim 21 in which saidcomposition includes an acid catalyst to encourage reaction of thehydroxy groups on said polyester resin with said aminoplast resin.
 24. Acoating composition as recited in claim 23 in which said compositionincludes a platinum catalyst to encourage reaction of the hydrogengroups of the hydrogen-functional polysiloxane with the vinyl groups inthe vinyl-terminated polysiloxane.
 25. A coating composition as recitedin claim 24 in which said composition includes an acid catalyst and aplatinum catalyst.
 26. A coating composition as recited in claim 25 inwhich said platinum catalyst is chloro platinic acid.
 27. A coatingcomposition as recited in claim 3 in which said composition includes ametal ion catalyst in which the metal is from the lead to manganeseelectromotive force series to encourage reaction of the hydrogen groupsof the hydrogen-functional polysiloxane with the hydroxy groups in thehydroxy-functional resin and the hydroxy groups in thehydroxy-functional polysiloxane.
 28. A coating composition as recited inclaim 27 in which said metal ion catalyst is dibutyl tin diacetate. 29.A coating composition as recited in claim 19 in which said coatingcomposition is entirely free of volatile organic solvent.
 30. A heatcurable coating composition which contains sufficient volatile organicsolvent to enable coating application and which is adapted to deposit arelease coating which stratifies to allow less polysiloxane to coat agiven surface area comprising:(1) a relatively viscoushydroxy-functional polyester resin; (2) a cross-linking agent for thepolyester; and (3) a mixture of at least two reactive polysiloxanescomprising:(A) a hydrogen- or alkoxy-functional polysiloxane in whichthe alkoxy group contains from 1-4 carbon atoms; and (B) a highmolecular weight elastomeric vinyl- or hydroxy-functional polysiloxanereactive with said hydrogen- or alkoxy-functional polysiloxane toprovide release properties,said vinyl- or hydroxy-functionalpolysiloxane being reactive with the cross-linking agent, and components(1), (2) and (3) being compatible in the solvent medium.
 31. A coatingcomposition as recited in claim 30 in which said hydroxy resin is apolyester which includes a component having a functionality of at least3.
 32. A coating composition as recited in claim 30 in which saidcross-linking agent is an aminoplast resin.
 33. A coating composition asrecited in claim 32 in which said aminoplast resin is hexamethoxymethylmelamine.
 34. A coating composition as recited in claim 32 in which saidcomposition includes an acid catalyst to encourage reaction of thehydroxy groups on said polyester resin and the hydroxy groups on saidpolysiloxane resin with said aminoplast resin.
 35. A coating compositionas recited in claim 30 in which the hydrogen groups of saidhydrogen-functional polysiloxane are reactive with the hydroxy groups inboth the polyester resin and the hydroxy-functional polysiloxane.
 36. Acoating composition as recited in claim 35 in which the reaction of thehydrogen groups of said hydrogen-functional polysiloxane is catalyzedwith a tin catalyst.
 37. A coating composition as recited in claim 36 inwhich said tin catalyst is dibutyl tin diacetate.
 38. A coatingcomposition as recited in claim 30 in which said polyester resin andsaid hydroxy-functional polysiloxane are highly viscous to solid at roomtemperature.
 39. A coating composition as recited in claim 30 in whichsaid hydroxy-functional polysiloxanes are dihydric dimethylpolysiloxaneshaving a room temperature viscosity in excess of about 3,000centipoises.
 40. A coating composition as recited in claim 30 in whichthe hydrogen groups of said hydrogen-functional polysiloxane arereactive with the unsaturated groups in both the polyester resin and thevinyl-functional polysiloxane.